1. Field of the Invention
The present invention relates to a band pass filter.
2. Description of Related Art
Along with the progress of technology, wireless communication systems such as cell phones, Bluetooth, cordless phone, wireless local area network (WLAN) are gradually popularized. The wireless communication system is mostly provided with a band pass filter, and mainly functions for allowing signals of the pass band to pass through, and filtering other interference signals except those of the pass band. In order to achieve a better filter effect, the resonance circuit is used to increase the transmission zero of the band pass filter, so as to increase the attenuation rate of the stop band (i.e. frequency bands other than the pass band). However, the resonance circuit usually causes the decrease of the response of the pass band, and the increase of the space required for the layout.